package com.seari;

public class IdWorker {


	    //下面两个每个5位，加起来就是10位的工作机器id
	    private long workerId;    //工作id
	    private long datacenterId;   //数据id
	    //12位的序列号
	    private long sequence;

	    public IdWorker(long workerId, long datacenterId, long sequence){
	        // sanity check for workerId
	        if (workerId > maxWorkerId || workerId < 0) {
	            throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0",maxWorkerId));
	        }
	        if (datacenterId > maxDatacenterId || datacenterId < 0) {
	            throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0",maxDatacenterId));
	        }
	        System.out.printf("worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
	                timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId);

	        this.workerId = workerId;
	        this.datacenterId = datacenterId;
	        this.sequence = sequence;
	    }

	    //初始时间戳
	    private long twepoch = 1288834974657L;

	    //长度为5位
	    private long workerIdBits = 5L;
	    private long datacenterIdBits = 5L;
	    //最大值
	    private long maxWorkerId = -1L ^ (-1L << workerIdBits);
	    private long maxDatacenterId = -1L ^ (-1L << datacenterIdBits);
	    //序列号id长度
	    private long sequenceBits = 12L;
	    //序列号最大值
	    private long sequenceMask = -1L ^ (-1L << sequenceBits);
	    
	    //工作id需要左移的位数，12位
	    private long workerIdShift = sequenceBits;
	   //数据id需要左移位数 12+5=17位
	    private long datacenterIdShift = sequenceBits + workerIdBits;
	    //时间戳需要左移位数 12+5+5=22位
	    private long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
	    
	    //上次时间戳，初始值为负数
	    private long lastTimestamp = -1L;

	    public long getWorkerId(){
	        return workerId;
	    }

	    public long getDatacenterId(){
	        return datacenterId;
	    }

	    public long getTimestamp(){
	        return System.currentTimeMillis();
	    }

	     //下一个ID生成算法
	    public synchronized long nextId() {
	        long timestamp = timeGen();

	        //获取当前时间戳如果小于上次时间戳，则表示时间戳获取出现异常
	        if (timestamp < lastTimestamp) {
	            System.err.printf("clock is moving backwards.  Rejecting requests until %d.", lastTimestamp);
	            throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds",
	                    lastTimestamp - timestamp));
	        }

	        //获取当前时间戳如果等于上次时间戳（同一毫秒内），则在序列号加一；否则序列号赋值为0，从0开始。
	        if (lastTimestamp == timestamp) {
	            sequence = (sequence + 1) & sequenceMask;
	            if (sequence == 0) {
	                timestamp = tilNextMillis(lastTimestamp);
	            }
	        } else {
	            sequence = 0;
	        }
	        
	        //将上次时间戳值刷新
	        lastTimestamp = timestamp;

	        /**
	          * 返回结果：
	          * (timestamp - twepoch) << timestampLeftShift) 表示将时间戳减去初始时间戳，再左移相应位数
	          * (datacenterId << datacenterIdShift) 表示将数据id左移相应位数
	          * (workerId << workerIdShift) 表示将工作id左移相应位数
	          * | 是按位或运算符，例如：x | y，只有当x，y都为0的时候结果才为0，其它情况结果都为1。
	          * 因为个部分只有相应位上的值有意义，其它位上都是0，所以将各部分的值进行 | 运算就能得到最终拼接好的id
	        */
	        return ((timestamp - twepoch) << timestampLeftShift) |
	                (datacenterId << datacenterIdShift) |
	                (workerId << workerIdShift) |
	                sequence;
	    }

	    //获取时间戳，并与上次时间戳比较
	    private long tilNextMillis(long lastTimestamp) {
	        long timestamp = timeGen();
	        while (timestamp <= lastTimestamp) {
	            timestamp = timeGen();
	        }
	        return timestamp;
	    }

	    //获取系统时间戳
	    private long timeGen(){
	        return System.currentTimeMillis();
	    }

	    //---------------测试---------------
	    public static void main(String[] args) {
	        IdWorker worker = new IdWorker(1,1,1);
	        
	        
	        for (int i = 0; i < 30; i++) {
	            System.out.println(worker.nextId());
	        }
	    }

	}

